Question

Nearsightedness is a recessive trait. If two nearsighted parents (male and female) give birth to four children, how many will be nearsighted?

1) 2
2) All
3) 1
4) 3
5) None

Answer 1

There's a likelihood of 2 out of 4 children being nearsighted if both parents carry the recessive trait for nearsightedness. Thus the correct option is 1.

Step-by-step explanation:

Nearsightedness being a recessive trait implies that an individual needs two copies of the nearsightedness allele (one from each parent) to exhibit the trait. Since both parents are nearsighted, they must carry two copies of the nearsightedness allele (nn). When these parents have children, each parent can only pass on one recessive allele (n) for nearsightedness, as they don't possess the dominant allele (N). Therefore, the offspring's genotype possibilities are: NN, Nn, or nn.

In this scenario, both parents are nn, meaning all their children will inherit at least one n allele. With each child having a 50% chance of inheriting the nn genotype (since both parents contribute an n allele), the probability of a child being nearsighted is 1 out of 2. In a family of four children, statistically, 2 out of 4 children are expected to inherit the nn genotype and hence exhibit nearsightedness. However, it's important to note that these are probabilities based on Mendelian inheritance and genetic principles; the actual outcome in any given family can vary due to chance. Thus the correct option is 1.